HYDROCLIMATE DEVELOPMENT FOLLOWING IMPOUNDMENT IN A TROPICAL AFRICAN MAN-MADE LAKE (LAKE ROBERTSON, ZIMBABWE)

Abstract

Lake Robertson was impounded by the Darwendale Dam which was completed in late 1976 to supplement the water supply to the City of Harare, Zimbabwe. This paper presents the results of a fortnightly sampling programme conducted on the lake between January 1976, when the lake began to form, and June 1977, when the lake was at full supply level. After an initial period of low oxygen saturation and high nutrient concentration, the lake rapidly attained stability as a warm, mesotrophic, polymictic impoundment. Factors contributing to this rapid stabilization included the lake morphometry which encouraged mixing (surface area = 81 km², mean depth - 6 m), the clearing of vegetation within the lake basin, and the rapid filling of the impoundment. The development of the lake hydroclimate is contrasted with similar patterns in other African man-made lakes and is shown to follow the classical pattern of Initial eutrophy followed by stability leading to maturity.